Hydroentangled filter media and method

ABSTRACT

A filter media formed in accordance with the present invention comprises hydroentangled, predominantly polyester staple length fibers having a basis weight of no more than about 12 oz/yd 2 . The filter media exhibits a Mullen burst strength of at least about 395 psi, and machine-direction and cross-direction shrinkage of less than about 3%, preferably less than about 2% . The filter media exhibits a machine-direction tensile strength of at least about 105 lb/in, and a cross-direction tensile strength of at least about 110 lb/in.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Ser. No. 10/050,413, filedJan. 16, 2002, which claims the benefit of priority ProvisionalApplication No. 60/262,229, filed Jan. 17, 2001, the disclosures ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to a nonwoven fabric employed asa filter media, and more particularly to a filter media comprising ahydroentangled nonwoven fabric, and a method of making the filter mediathrough the use of a formaninous surface.

BACKGROUND OF THE INVENTION

Filtration of fluids such as gases requires the removal of typicallyparticulate or disparate impurities from the gas stream in order tolimit introduction of the impurities into the environment, orcirculation back into the associated process. It is ordinarily desirableto maximize the surface area available for filtration so as to removelarge amounts of undesirable contaminants from the fluid stream, whilemaintaining the operating pressure differential induced by the filter aslow as possible to achieve long service life and minimize surfacestrain.

One form of filtration is typically referred to as interception, thatis, the filter media functions in the nature of a sieve thatmechanically entraps particles larger than the pore size inherent to themedia. Larger particles are removed from the fluidic stream by theopenings in the filter media, with particles building on top of oneanother to create a filter cake that removes successively smallerparticles.

More specifically, in a so-called “baghouse filter”, particulatematerial is removed from a gaseous stream as the stream is directedthrough the filter media. In a typical application, the filter media hasa generally sleeve-like tubular configuration, with gas flow arranged soas to deposit the particles being filtered on the exterior of thesleeve. In this type of application, the filter media is periodicallycleaned by subjecting the media to a pulsed reverse-flow, which acts todislodge the filtered particulate material from the exterior of thesleeve for collection in the lower portion of the baghouse filterstructure. U.S. Pat. No. No. 4,983,434, hereby incorporated byreference, illustrates a baghouse filter structure and a prior artfilter laminate.

Heretofore, nonwoven fabrics have been advantageously employed formanufacture of filter media. Generally, nonwoven fabrics employed forthis type of application have been entangled and integrated bymechanical needle-punching, sometimes referred to as “needle-felting”,which entails repeated insertion and withdrawal of barbed needlesthrough a fibrous web structure. While this type of processing acts tointegrate the fibrous structure and lend integrity thereto, the barbedneedles inevitably shear large numbers of the constituent fibers, andundesirably create perforations in the fibrous structure, which act tocompromise the integrity of the filter and can inhibit efficientfiltration. Needle-punching can also be detrimental to the strength ofthe resultant fabric, requiring that a suitable nonwoven fabric have ahigher basis weight in order to exhibit sufficient strength forfiltration applications.

U.S Pat. No. 4,556,601 to Kirayoglu discloses a hydroentangled, nonwovenfabric, which may be used as a heavy-duty gas filter. This filtrationmaterial however, cannot be subjected to a shrinkage operation. Exposureof the described fabric to a shrinkage operation is believed to have anegative effect on the physical performance of the filtration material.

The present invention is directed to a filter media, and method ofmaking, which is formed through hydroentanglement, thus avoiding thedeleterious effects of mechanical needling, while providing a filtermedia having the requisite strength characteristics, without possessinga limiting factor in performance. The filtration media of the presentinvention also demonstrates a highly desirable uniformity forcost-effective use.

SUMMARY OF THE INVENTION

A filter media formed in accordance with the present invention compriseshydroentangled, predominantly polyester staple length fibers having abasis weight of no more than about 12 oz/yd². The filter media exhibitsa Mullen burst strength of at least about 395 psi, and machine-directionand cross-direction shrinkage of less than about 3%, preferably lessthan about 2%. The filter media exhibits a machine-direction tensilestrength of at least about 105 lb/in, and a cross-direction tensilestrength of at least about 110 lb/in.

The present filter media is formed by providing a precursor webcomprising predominantly staple length polyester fibers. The presentmethod further comprises providing a foraminous surface, which may beconfigured to impart a repeating pattern to the filter media beingformed for enhancing its filtration capabilities. The precursor web ispositioned on the foraminous surface, and hydroentangled to form thepresent filter media in the form of a nonwoven fabric.

It is within the purview of the present invention that the filter mediabe heat-set subsequent to hydroentangling. By the inclusion of fusiblefibers in the precursor web, heat-setting of the filter media candesirably result in thermal bonding of the media, thus enhancing thestrength characteristics of the material.

Other features and advantages of the present invention will becomereadily apparent from the following detailed description, theaccompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 a diagrammatic view of an apparatus for manufacturing filtermedia embodying the principles of the present invention; and

FIG. 2 is a diagrammatic view of a baghouse filter arrangement for whichthe baghouse filter media of the present invention is particularlysuited for use.

DETAILED DESCRIPTION

While the present invention is susceptible of embodiment in variousforms, there is shown in the drawings, and will hereinafter bedescribed, a presently preferred embodiments, with the understandingthat the present disclosure is to be considered as an exemplification ofthe invention, and is not intended to limit the invention to thespecific embodiments illustrated.

The present invention described herein includes the uses ofhydroentangled nonwovens as described below, is a direct replacement forneedled felts in all such applications where such materials arecurrently used. These applications include air filtration in tubular andsheet form, used in air handling, as represented by baghouse stations,liquid filtration systems, and automatic transmission fluid filters, andother specialty applications where needled felts are employed.

With particular reference to FIG. 1, therein is illustrated an apparatusfor practicing the method of the present invention for forming anonwoven fabric. The fabric is formed from a fibrous matrix, whichcomprises fibers selected to promote economical manufacture. Thefibrousmatrix is preferably carded and subsequently cross-lapped to forma precursor web, designated P.

FIG. 1 illustrates a hydroentangling apparatus for forming nonwovenfabrics in accordance with the present invention. The apparatus includesa foraminous-forming surface in the form of a flat bed entangler 12 uponwhich the precursor web P is positioned for pre-entangling. Precursorweb P is then sequentially passed under entangling manifolds 14, wherebythe precursor web is subjected to high-pressure water jets 16. Thisprocess is well known to those skilled in the art and is generallytaught by U.S. Pat. No. 3,485,706, to Evans, hereby incorporated byreference.

The entangling apparatus of FIG. 1 further includes an imaging andpatterning drum 18 comprising a foraminous surface for effecting imagingand patterning of the now-entangled precursor web. After pre-entangling,the precursor web is trained over a guide roller 20 and directed to theimage transfer device 18, where an image and/or pattern is imparted intothe fabric on the foraminous-forming surface of the device. The web offibers is juxtaposed to the foraminous surface 18, and high pressurewater from manifolds 22 is directed against the outwardly facing surfacefrom jet spaced radially outwardly of the foraminous surface 18. Theforaminous surface 18, and manifolds 22, may be formed and operated inaccordance with the teachings of commonly assigned U.S. Pat. No.5,098,764, No. 5,244,711, No. 5,822,823, and No. 5,827,597, thedisclosures of which are hereby incorporated by reference. It ispresently preferred that the precursor web P be given an image and/orpattern suitable to provide fluid management, as will be furtherdescribed, to promote use of the present nonwoven fabric in filtrationmedia. The entangled fabric can be vacuum dewatered at 24, and dries atan elevated temperature on drying cans 26.

With reference to FIG. 2, therein is diagrammatically illustrated arepresentative baghouse filter structure for use with the filter mediaof the present invention. This type of baghouse filter structure istypically employed in industrial applications requiring filtration ofparticulate material from a fluidic stream. As illustrated, the fluidicstream enters a filter chamber, within which, one or more generallytubular, sleeve-like filter bags are arranged. Gas flows through theexterior surface of the filter bags by the creation of a pressuredifferential across the filter media, with particulate material removedfrom the gaseous stream as the material lodges against the filter media.Typically, the particulate material is dislodged from the exterior ofthe filter bags by periodically subjecting each filter bag to pulsedreverse-flow of fluid, whereby the particulate material, typicallyreferred to as filter cake, is forced from the exterior of each filterbag, and collected at a lower portion of the structure.

The baghouse filter media embodying the principles of the presentinvention may be configured as a filter bag illustrated in FIG. 2. Forsuch applications, the filter media may be formed as a planar sheet,with opposite edges joined to form an open-ended tube. The tube can thenbe closed at one end to form a sleeve-like bag, as illustrated in FIG.2. For other applications, the filter media may be employed in itsplanar form, or in the form of an open-ended tube.

Other potential filtration applications besides baghouse filtrationinclude HVAC filtration, wherein a frame with a filter media is placedin the path of the flow of air to remove particles such as dust from theair before the air is circulated into a room. Food and beveragefiltration is another application, whereby a filter may be placed beforeor after the fluid contacts the beverage making substances in order toremove contaminants from the fluid. Coalescing filtration is yet anotherapplication, such as used in diesel engines and marine applications.Coalescing filter media are commonly employed within a frame and housinglocated either upstream or downstream of the liquid hydrocarbon pump.Still other potential filtration applications include vacuum filterequipment, mist elimination, turbine intake filtration, automotive andtruck transmission and air in-take filtration, coolant filtration,chemical filtration, including medical and pharmaceutical filtration,power generation filtration, office equipment filtration, paper machineclothing felt and drain layer filtration, as well as filtrationapplications.

Filter media embodying the principles of the present invention is formedby hydroentanglement on a foraminous surface, such as disclosed in U.S.Pat. No. 5,244,711, to Drelich et al., hereby incorporated by reference.Depending upon the specific configuration of the foraminous surface, thefibrous material may have a repeating pattern imparted in the plane ofthe fabric or the repeating pattern may protrude from the plane of thefabric. A foraminous surface for practicing the present inventiontypically includes a meshed surface such as a screen, or an imagetransfer device having a pronounced three-dimensional topography wherebythe high-pressure liquid (water) streams directed at the fibrousmaterial for hydroentanglement can pass through the foraminous surface.

Formation of a filter media in accordance with the present invention iseffected by providing a precursor web of predominantly staple lengthpolyester fibers selected to have a basis weight corresponding to thebasis weight of the filter media being formed. In accordance with thepresent invention, the present filter media preferably has a basisweight of no more than about 12 oz/yd², thus facilitating efficientfabrication by hydroentanglement, and cost-effective use of the fibrousmaterial from which the media is formed.

Depending upon the composition of the precursor web from which thepresent filter media is formed, the strength and integrity of thematerial can be desirably enhanced. By incorporation of fusible fibers,such as sheath fibers or bi-component thermoplastics includingpolyesters, polyamides, and/or polyolefins, it is possible to effectheat-bonding of the fiber structure during heat-setting of the material,subsequent to hydroentanglement. Further, it has been found that in theabsence of specific fusible fibers, heat-setting of the material candesirably enhance the strength and the porosity of the nonwoven fabricto improve its filtration characteristics.

By configuring the foraminous surface employed during hydroentanglementto impart a specifically-configured pattern to the filter media,filtration characteristics of the media can be further enhanced,including an increase in the effective surface area, improvement infilter cleaning efficiency, and to alteration of depth filtrationperformance. As will be appreciated, this is a distinct advantage incomparison to conventional needle-punched fabrics, which ordinarilycannot be meaningfully imaged in connection with mechanicalentanglement. Use of 100% polyester staple length fibers is presentlycontemplated, as well as use of 90% polyester fibers in combination with10% fusible sheath fibers. The fabric weight is selected to be no morethan about 12 oz/yd², preferably on the order of about 10 oz/yd².

Notably, formation of the filter media of the present invention byhydroentanglement has been found to desirably provide the filter mediawith the requisite strength characteristics, and resistance toshrinkage. Filter media formed in accordance with the present inventionis suitable for application in such industries as mining, cement,chemical, iron and steel, utilities, and work with carbon black. Thedisclosed filter media of the present invention preferably exhibits aMullen burst strength of at least about 395 psi, with machine-directionand cross-direction shrinkage of less than about 3%, and morepreferably, less than about 2%. The filter media preferably exhibits amachine-direction tensile strength of at least about 105 lb/in, and across-direction tensile strength of at least about 110 lb/in, inaccordance with ASTM D461-93, Section 12.

The accompanying Table sets forth performance characteristics for filtermedia formed in accordance with the present invention in comparison to aconventional needle-punched nonwoven fabric having a basis weight of 16oz/yd2, designated and commercially available Menardi 50-575. As thetest results indicate, a filter media formed in accordance with thepresent invention exhibits performance comparable to that achieved withthe needle-punched fabric, notwithstanding the significant difference inbasis weights of the two fabrics.

From the foregoing, numerous modifications and variations can beeffected without departing from the true spirit and scope of the novelconcept of the present invention. It is to be understood that nolimitation with respect to the specific embodiments disclosed herein isintended or should be inferred. The disclosure is intended to cover, bythe appended claims, all such modifications as fall within the scope ofthe claims. Physical/Performance Properties Menardi 50-575 Manardi50-575 Scale Sample CLC-135 (4/4/00) Sample (8/29/00) Physicals TestMethod Worst/Best Specification (4/4/00) NL-A2-C-00-098-004- Tested10/12/00 Fiber Composition PET - PET - PET - T203 PET 2.25 dpf 2.25 dpfMechanical/Chemical Heatset, Heat Set, None Finish Plain Finish SingedBasis Weight (oz/sy) ASTM D461-93 se. 11 14.5-16.5 15.5 10.2 16.1Thickness (mas) ASTM D461-93 sec. 10 65-85 75.6 57.75 72.4 Frazier AirPermeability ASTM D461-93 sec. 18 30-45 35.6 38.8 31.4 (cfm @0.5″ H20)Jullen Burst (psi) ASTM D461-93 sec. 13 More is Better >400 411 538Tensiles - MD 1″ Strip (lb/in) ASTM D461-93 sec. 12 More is Better >75104 139.1 106.45 Tensiles - CD 1″ Strip (lb/in) ASTM D461-93 sec. 12More is Better >150 169 110.4 192.81 Elongation - MD 1″ Strip (%) ASTMD461-93 sec. 12 94 43.5 97 Elongation - CD 1″ Strip (%) ASTM D461-93sec. 12 79 71.1 92 Tensiles - MD GRAB (lb/in) TM-7012 More is Better260.14 Tensiles - CD GRAB (lb/in) TM-7012 More is Better 267.84 283.43283.37 Elongation - MD GRAB (%) TM-7012 58.21 207.01 405.6 Elongation -CD GRAB (%) TM-7012 50.17 42.99 45.91 Elongation - MD @ 10 lbs/ SpecialTest Less is Better <5 2.45 61.91 25.27 2 in width load (%) Elongation -CD @ 10 lbs/ Special Test Less is Better <5 4.25 1.33 5.46 2 in widthload (%) Coulter Pore Size Distribution - 28 5.2 5.42 MFP (microns)Coulter Pore Size Distribution - 58 19.55 Max (microns) Very wide spread(>50) of only 41.43 2 data points PMI Pore Size Distribution - 21.8318.07 18.08 MFP (microns) PMI Pore Size Distribution - 67.1 42.32 52.72Max (microns) PMI Pore Size Distribution - 1.17 1.91 1.29 Min (microns)Shrinkage - MD 2 hrs @ Less is Better 0.5 0.5 300 F. (%) Shrinkage - CD2 hrs @ Less is Better 0 0 300 F. (%) Shrinkage - MD 24 hrs @ Less isBetter <3 1.5 1 350 F. (%) Shrinkage - CD 24 hrs @ Less is Better <3 0.50 350 F. (%) Liquid Filtration Efficiancy (%) 86.6 90.6 91.4 for CoarseDust Liquid Filtration Life/Weight 3.12 4.21 3.87 Gain (min) for CoarseDust Liquid Filtration Life/Weight 26.13 41.5 27 Gain (%) for CoarseDust Liquid Filtration Efficiency (%) 45.43 54 60.7 for Fine Dust LiquidFiltration Life/Weight 6.6 6.06 5.51 Gain (min) for Fine Dust LiquidFiltration Life/Weight 27.03 44.4 22.4 Gain (%) for Fine Dust 100 cyclesBaghouse Filtration Test (FEMA) from ETS, INC Outlet emmissions (mg/m3)Less is Better 7.14 2.4 1.89 Residual DeltaP Change (Pa) Less is Better159.7 178.8 325.5 Average Residual DeltaP (Pa) Less is Better 169.88178.85 285.9 Average Cycle Time (seconds) More is Better 56 66 40 FabricWeight Gain (grams) Less is Better 1.15 1.26 1.37 Mullen Burst (psi)More is Better 505 395 555 Manardi 50-57S Sample (8/29/00) BHF1030-#4BHF1030-#5 Physicals PH0829 (8/29/00) Tested 11/28/00 BHF1030-#1(0.676EE) (140 bar) Fiber Composition PET - T472 PET - T203 PET - T203PET - T203 1.5 dpf 1.5 dpf 1.5 dpf 1.5 dpf Mechanical/Chemical None NoneNone None Finish Basis Weight (oz/sy) 10.06 10.2 10.2 10.16 Thickness(mas) 65.4 65.5 59.4 63 Frazier Air Permeability 36.6 42.2 38.3 41.6(cfm @0.5″ H20) Jullen Burst (psi) 400 411 394.3 405 Tensiles - MD 1″Strip (lb/in) 126.99 127.2 124.1 125.3 Tensiles - CD 1″ Strip (lb/in)85.5 123.8 120.3 121.8 Elongation - MD 1″ Strip (%) 43 53 46.5 54Elongation - CD 1″ Strip (%) 100 59 65.4 67 Tensiles - MD GRAB (lb/in)289.68 255.8 250.9 252.3 Tensiles - CD GRAB (lb/in) 191.63 236.6 237237.5 Elongation - MD GRAB (%) 40.73 33.13 31.8 32.6 Elongation - CDGRAB (%) 35.29 30.44 29.8 30.5 Elongation - MD @ 10 lbs/ 2.1 2.4 2 inwidth load (%) Elongation - CD @ 10 lbs/ 11.05 2.5 2 in width load (%)Coulter Pore Size Distribution - MFP (microns) Coulter Pore SizeDistribution - Max (microns) Very wide spread (>50) of only 2 datapoints PMI Pore Size Distribution - 18.99 19.49 18.49 MFP (microns) PMIPore Size Distribution - 47.53 54.87 43.21 Max (microns) PMI Pore SizeDistribution - 2.05 1.98 1.6 Min (microns) Shrinkage - MD 2 hrs @ 0.50.5 0.67 300 F. (%) Shrinkage - CD 2 hrs @ 0 0 0 300 F. (%) Shrinkage -MD 24 hrs @ 1.5 1.5 1.5 350 F. (%) Shrinkage - CD 24 hrs @ 0.5 0.5 0 350F. (%) Liquid Filtration Efficiancy (%) 90 90.6 79.6 for Coarse DustLiquid Filtration Life/Weight 3.88 3.17 6.12 Gain (min) for Coarse DustLiquid Filtration Life/Weight 40.8 25.8 57.6 Gain (%) for Coarse DustLiquid Filtration Efficiency (%) 71.1 60.6 53.9 for Fine Dust LiquidFiltration Life/Weight 4.81 4.45 7.54 Gain (min) for Fine Dust LiquidFiltration Life/Weight 33 22.4 48.1 Gain (%) for Fine Dust 100 cyclesBaghouse Filtration Test (FEMA) from ETS, INC Outlet emmissions (mg/m3)7.8 8.08 2.53 Residual DeltaP Change (Pa) 189.1 311.2 212.5 AverageResidual DeltaP (Pa) 194.4 289.8 207.4 Average Cycle Time (seconds) 6838 59 Fabric Weight Gain (grams) 0.96 0.89 1.1 Mullen Burst (psi) 425535 385

1. A method of making a filter media comprising the steps of: providinga precursor web comprising predominant staple length polyester fibers;providing a foraminous surface, and positioning said precursor web andsaid foraminous surface; and hydroentangling said precursor web to formsaid filter media, said filter media having a basis weight of no morethan about 12 oz/yd², and exhibiting a Mullen burst strength of at leastabout 395 psi, and machine-direction and cross-direction shrinkage ofless than about 3%.
 2. A method of making a filter media in accordancewith claim 1, wherein said foraminous surface is a three-dimensionalimage transfer device.
 3. A method of making a filter media inaccordance with claim 1, including: heat-setting said filter media aftersaid hydroentangling step.
 4. A method of making a filter media inaccordance with claim 2, wherein said precursor web comprises fusiblefibers whereby said filter media is thermally bonded during saidheat-setting step.
 5. A filter media comprising hydroentangled,predominant polyester staple length fibers having a basis weight of nomore than about 12 oz/yd², a Mullen burst strength of at least about 395psi, and machine-direction and cross-direction shrinkage of less thanabout 3%.
 6. A filter media in accordance with claim 4, wherein saidmedia exhibits machine-direction and cross-direction shrinkage of lessthan about 2%.
 7. A filter media in accordance with claim 4, whereinsaid filter media exhibits a machine-direction tensile strength of atleast about 105 lb/in and a cross-direction tensile strength of at leastabout 110 lb/in.
 8. A filter media in accordance with claim 1, whereinsaid filter media is a gas filter.
 9. A filter media in accordance withclaim 1, wherein said filter media is an air filter.
 10. A filter mediain accordance with claim 1, wherein said filter media is a liquidfilter.